Vinylidene chloride interpolymers are well-known in the prior art. In the past, vinylidene chloride interpolymers have been produced by an emulsion or suspension polymerization process. Both the emulsion and suspension polymerization processes produce an aqueous dispersion of polymer particles having a relatively small particle diameter. The polymer particles are recovered from the aqueous dispersion by drying or other means for removing a majority of the aqueous phase. In the past, the practice has been to extrude the vinylidene chloride interpolymer directly from the form in which it is recovered.
In some instances, it is desirable to form the vinylidene chloride interpolymer into pellets prior to final extrusion. Unfortunately, it has been found that vinylidene chloride interpolymers are not easily extrudable. Attempts to extrude vinylidene chloride interpolymers on certain extrusion equipment have proven unsatisfactory due to the adhesion of the resin to interior walls of the extruder, which leads to an excessively long polymer residence time and an undesirable level of carbon contamination in said pellets.
Vinylidene chloride interpolymers are well-known for their excellent barrier to mass transport of atmospheric gases and moisture vapor. These interpolymers have limited areas of application, however, because of poor melt processing characteristics. In particular, vinylidene chloride interpolymers in a melt plasticized state have poor heat stability and low melt strength. These same interpolymers, when fabricated, tend to be brittle and to have low impact strength.
Similarly, thermoplastic graft copolymers are well-known in the prior art. Such rubbers are well-known for their excellent physical properties. Specifically, thermoplastic graft copolymers possess relatively high impact strength. Unfortunately, thermoplastic graft copolymers provide a relatively low degree of barrier to mass transport of atmospheric gases and water vapor when compared to vinylidene chloride interpolymers.
It would be desirable to produce a polymeric polyblend possessing a good balance of physical properties.
It is further desirable to produce a vinylidene chloride interpolymer which interpolymer is capable of being extruded without producing an unacceptable level of carbon contamination. It is to this goal that the present invention is directed.